Wind environment researches have been performed for analyzing a diffusion status of exhaust gas from a factory, or for analyzing air currents around buildings in the vicinity of a large structure such as a bridge or a building before constructing the structure for the prediction of wind damage and countermeasures against the damage. For the research, a method of performing measurement in an actual site has been used. However, in terms of cost, a method of performing analysis through a wind tunnel test using a scale model of geographical features is widely used.
The wind tunnel instrument is classified into a closed-circuit type and an open-circuit type. The closed-circuit type has less power loss but requires a large space and high cost. So, it is suitable for a high-quality experiment with high wind velocity and low turbulence. The open-circuit type has an advantage of a small space and low installation cost, however, has high power loss. So, it is suitable for a low-quality experiment with low wind velocity and high turbulence on constructions and buildings.
FIG. 1 illustrates an example of the closed-circuit wind tunnel instrument, but the open-circuit wind tunnel instrument is also configured similarly. The close-circuit wind tunnel instrument includes: a blower 20 for blowing wind; a diffuser 30 which has an increased cross-section to decrease a velocity of air current from the blower 20 thereby enhancing a rectifying function of a settling chamber; a settling chamber 40 for decreasing a turbulence strength and suppressing a velocity component in an axial direction through a rectification lattice; a contraction 50 which has a decreased cross-section to increase velocity and form uniform air current with constant pressure and velocity; a test unit 10 for performing various measurements; and other measurement devices and a controlling device.
A vertical profile of wind blowing on an actual ground surface is changed according to a roughness of the ground surface (surface roughness) and height as shown in the following boundary layer equation. Trees and buildings existing on the actual ground surface increase the surface roughness of the ground surface, and the wind blowing on the actual ground surface has a relatively smaller velocity than that blowing at a higher position as shown by a vertical profile illustrated in FIG. 2.
                    u        =                                            u              *                        k                    ⁢                      ln            ⁡                          (                              z                                  z                  0                                            )                                                          [                  Equation          ⁢                                          ⁢          1                ]            
where
u*: friction velocity,
k: Von Kámán constant, and
z0: roughness height.
In order to provide an environment similar to the actual geographical features, the wind tunnel instrument is given a roughness for the ground surface by installing an arbitrary standing object 11 as illustrated in FIG. 2.
However, in this method, in order to create the boundary layer, a large section including the standing object 11 has to be provided on a front portion of the test unit 10. In addition, since the ground surface condition changes whenever a new wind experiment research is needed, there is a problem in that the test unit of the wind tunnel instrument has to be newly constructed. Furthermore, there is a problem in that large space and high costs are needed.
Also, there are many difficulties in the existing method to form an exact shape of a wind profile desired by the experimenter.